1. Field of the Invention
This invention relates to drive pulleys, and in particular to variable drive pulleys.
2. Description of the Background Art
In one conventional form of variable pulley known in the art, a pair of sideplates defining confronting conical belt-engaging surfaces are mounted to a shaft by splines, or keyways. At least one of the sideplates is movable along the shaft to provide a variable spacing between the conical belt-engaging surfaces, thereby to provide the variable drive. The provision of the splines, or keyways, has presented manufacturing problems in that such manufacture has required expensive materials and high manufacturing costs. Additionally, such pulley construction has had the serious disadvantage of high stress produced in the splines and keyways. Such stress has caused substantial wear and heating of the structure resulting in increased sliding resistance and shortened useful life of the structure.
In one prior art variable pulley structure illustrated in Japanese Utility Model Publication No. 35421/1977, one of the movable sideplates of the variable pulley is engaged by a coil spring. The opposite ends of the coil spring are bent and retained at one end in a recess provided in the movable sideplates and at the other end in a part of the shaft. Rotation of the pulley in use of the drive urges the coil spring in a winding direction. Repeated rotational pulses applied to the spring as a result of torque variations in the operation of the drive system have often resulted in breaking of the spring, particularly at the connections to the sideplate and shaft.